MMAE 370 LAB#4: Experiment Design-Testing the Mechanical Pro

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Experiment Design - Testing the Mechanical Properties of Carbon fiber as a Function of Fiber Orientation

Specific Stiffness: Ratio of elastic modulus of material to its mass densityCharacteristic of low-weight, high strength materials that find applications in the aerospace and automotive industry.From the results obtained in the lab, there seems to be a strong correlation in the relationship between fiber direction, manufacturing methods and stiffness.IntroductionComposite material: Combination of two or more chemically distinct and insoluble phases with recognizable interface such that its properties and structural performance are superior to those of the constituents acting independentlyFiber composites: consists of fibers in polymer matrixHas high specific strength (strength to weight ratio) and specific stiffness (stiffness to weight ratio) Highly anisotropic (direction dependent)Highest stiffness and strength when fibers align in direction of tension forceChallenges of creating complex structures out of compositesControlling environmentFollowing strict standardsie: eliminating voids

AbstractProposed lab experiment to test the anisotropic behavior of carbon fiber when layered in different orientations in a bending test.Additionally analyze the effect of certain manufacturing methods on the stiffness of the materialSandwich: It is composed of facings, a firm core and adhesive.3 point Bending Test:Loading at 3 points, used to analyze Elastic modulus of the sandwich. Best way to measure the properties of the sandwich since one facing is in tension, the other in compression and shearing in core.Testing for properties 3 point or 4 point bending testcommon testing method for brittle materialsLoad is applied vertically to either:One point= three-point bending (a)Two points= four-point bending (b)Upper surface= compressive stressLower surface = tensile stress Stress calculated using simple bean equationStress at fracture of bending = modulus of rupturefour-point test gives a lower modulus of rupture than the three-point Carbon fiber aluminum honeycomb sandwichReason for ExperimentCarbon fiber electric car for lightness and equivalent strength of steelThis needs to be proved for SAE Formula competitionOrientation of fibers is looked at to reduce weight even furtherStronger panels are used in areas of the car that actually need impact protection, helping minimize weight and optimize on track performanceSandwich structureComposite made of stiff skins with a low density coreMetal matrix materials in core: aluminum, aluminum-lithium alloy (lighter than aluminum), magnesium, copper, titanium, and super alloysFiber skin materials: graphite, boron, alumina, silicon carbide, molybdenum, and tungsten

ProcedureMany materials are used in the layup process (next slide)CYCOM 5320-1HEXCEL 5052 Aluminum coreCarbon fiber stored in freezer for longer shelf lifeMaterials needed to be cut prior to layupTemplate used for the bending testOversized template was also used so edges could be cut offASTM C393 changed to fit Formula SAE competition rules

The layup processVacuum checkDon’t lose more than 2in Hg of vacuum in 5 minutesCuringRamped 5 deg F per minute to 250, hold for 3 hoursRaised then to 350, held for 2 hours for post-cureCutting with abrasive tile cutting saw

3 point bending test in actionResultsTable of Validity of bending tests

Calculations of specific stiffnessEquations Measurements

Elastic modulus calculations and results plotFiber orientation plot

Differences in procedure plot

Error analysisLoss of vacIncrease of mass, possibly due to moisture contentFailure of facingDifferences in highest point used to calculate stiffnessUncertainty of failure modeMost likely failed due to shear of the core because when the double adhesive sample was tested, the strength was the same

DiscussionThere is a definite relation between fiber orientation and stiffness. In general, stiffness is greatest when oriented in direction of fibersManufacturing method also affected stiffnessNot very much difference in vac vs no vacCore orientation increased stiffnessDouble film adhesive also increased stiffnessIt is important to follow procedure carefully because it can greatly affect the end product

ConclusionsSAE – orient the carbon fiber to maximize strength and stiffness in certain directions to save weightUsed in the aerospace industry for light weight and high stiffness